Field of the Invention
The present invention relates to power transmission devices and power reception devices, and more particularly to detection of a foreign object between a power transmission device and a power reception device that exchange electric power in a contactless manner.
Description of the Background Art
There have been proposed a variety of contactless electric power transfer systems in which electric power is transferred from a power transmission device to a power reception device in a contactless manner.
In such a contactless electric power transfer system, it is expected that a foreign object (an object that should not be present) will enter between the power transmission device and the power reception device, and it is necessary to properly detect the foreign object. For example, Japanese Patent Laying-Open No. 2013-27171 discloses a detection device capable of accurately detecting a metallic foreign object even during power transmission from a power transmission device to a power reception device. This detection device detects a metallic foreign object present between the power transmission device and the power reception device based on a change in Q factor of a resonant circuit including a coil. This coil for Q factor measurement may be provided separately from a power feeding coil (a power transmission coil or a power reception coil), or the power feeding coil may be used as this coil.
In the detection device described in Japanese Patent Laying-Open No. 2013-27171, the power feeding coil may be used as the coil for Q factor measurement, and if the coil for Q factor measurement is provided separately from the power feeding coil, the coil for Q factor measurement is expected to have a similar size to the power feeding coil. However, in a system handling high power such as a contactless power feeding system of a vehicle, for example, the power feeding coil increases in size to some extent which may result in inability to detect a relatively small foreign object compared to the power feeding coil.